One type of color image display device is a liquid crystal display that displays an image using in combination a backlight and a liquid crystal panel which controls the transmittance of a liquid crystal at each pixel location (hereinafter, pixel). For display of a color image, the backlight includes at least three color light sources of red, green, and blue, and each of pixels in the liquid crystal panel includes sub-pixels at which three color filters of red, green, and blue are disposed. The transmittances of a liquid crystal at respective sub-pixels with red, green, and blue color filters are controlled in order to control the quantities of backlight emitted from the red, green, and blue light sources, whereby an image is displayed.
The sub-pixel signifies the smallest unit pixel location at which any of red, green, and blue color filters is disposed. Three sub-pixels at which three color filters of red, green, and blue respectively are disposed are combined in order to construct a pixel. A plurality of pixels are disposed in order to construct a screen.
The principles of display will be briefed below. The quantities of backlight emitted from three color light sources are adjusted based on the transmittances of a liquid crystal at respective sub-pixels, whereby shades to be displayed at respective sub-pixel can be controlled. Color filters are disposed at respective sub-pixel so that the shades of red, green, and blue can be displayed. The display output is calculated as a product of the quantities of backlight by the transmittances of the liquid crystal. Herein, a gamma that is not proportional to or independent of a wavelength. Herein, however, data is proportional to or dependent on a wavelength.
Assuming that a fluorescent lamp is adopted as a backlight and lit all the time, since a quantity of backlight remains constant, variables to be employed in the above multiplication are the transmittances of the liquid crystal at respective sub-pixels.
Patent Document 1 describes a constituent feature of improving a contrast by controlling a quantity of backlight. In this case, a display output represents the result of a multiplication employing as variables the quantity of backlight and the transmittance of the liquid crystal panel. Herein, the maximum and minimum values of a display signal are referenced as factors with which the quantity of backlight is controlled.
Moreover, Patent Document 2 describes that the wavelength regions of light waves emitted from a backlight and the passbands of color filters at respective sub-pixels are taken into consideration. Herein, the wavelength regions of light waves emitted from the backlight are made narrower than the passbands of the color filters, whereby a color domain is expanded. The backlight comprises light-emitting diodes (LED).
[Patent Document 1] Japanese Patent No. 3430998
[Patent Document 2] Japanese Unexamined Patent Publication No. 60-130715
In the background art, image quality is improved by devising a backlight. However, the background art is not intended to reduce energy (power consumption) required for driving the backlight.
Patent Document 1 introduces a constituent feature of varying a quantity of backlight. However, an object is to improve the contrast of a display screen but no consideration is taken into a power consumption. Moreover, Patent Document 2 describes a constituent feature of improving image quality using a backlight comprising LEDs. However, no consideration is taken into the power consumption. Both Patent Document 1 and Patent Document 2 do not take account of reducing energy (power consumption) to be consumed by the backlight.
In the course of solving the foregoing problems, a phenomenon of a leakage (crosstalk) of red, green, or blue poses as an obstacle to be overcome. Assuming that the wavelength regions of light waves emitted from LEDs included in a backlight are inconsistent with the passbands of color filters incorporated in a liquid crystal panel, the aforesaid multiplication cannot be achieved relative to each of red, green, and blue. Consequently, two of red, green, and blue correlate with each other. This brings about the crosstalk.
Patent Document 1 makes it a precondition to adopt a fluorescent lamp as a white light source but does not take account of the wavelength region of emitted light. Moreover, Patent Document 2 describes that LEDs are adopted as white light sources whose light waves exhibit peaks at wavelengths representing respective primary colors of red, green, and blue, but does not take account of the variation of the wavelength regions of light waves emitted from the LEDs. The second object of the present invention is to cope with a newly arisen problem of a crosstalk.